1. Field of the Invention
The present invention relates to encoding and decoding of video images and more particularly to manipulating parameters of an encoding engine to minimize impact on encoded data rates while servicing update requests for retransmission of lost data.
2. Description of the Related Arts
As the Internet becomes more and more popular, more and more data are being transferred using the Internet. The internet and other channels of communication have bandwidth limitations. Data compression is often used to maximize data transmission over such limited bandwidth channels. Most people access the Internet using fixed rate channels such as telephone lines. The fixed rate channels present problems for viewing video. Typically, as video images are compressed, the video compression process generates a variable data rate over time. The variable data rate is undesirable for fixed rate channels and often causes jittery video images at the receiver.
Furthermore, transmission errors often occur whenever data is transferred over a lossy medium such as a telephone line as is the case when images are encoded as compressed data sent over the telephone line or other network and decoded to reveal the original images. When decoded erred images cannot be ignored through error correction techniques or interpolation of surrounding images, retransmission of the erred images are needed for smooth video images. However, retransmission of erred images increases the amount of compressed data for a codec (encoding and decoding) system. Not only is there compressed data from encoded incoming images, there is also compressed data from retransmission of the erred data. Increasing the overall data rate may also produce undesirable effects to the video images at the receiver. In current systems lost data results in the need to transmit an intra frame to refresh the decoded image. Intra frames require 3-5 times the bandwidth usually allowed per frame. Frequent transmission of intra frames results in a significant reduction in frame rate and an inability to represent motion in the input images.
Therefore, it is desirable to provide an apparatus and methods of operating the same which maintains a target data rate while servicing update request for retransmission of erred images.